Enchanting skills starts at the third class change (lvl 76) so you've got a while before then. Basically it allows you to change certain parts of some of your skills. Cast time, power, duration, etc.
Sealed items do not give the set bonus when worn. They must be unsealed either with Ancient adena or if its B grade you need to see the blackmarket mammon guy. Can see more about the set bonuses in the library. (http://www.lineage2.com/Knowledge/item_sets.html)
Some jewelry (A and S grade) can also be unsealed to give aditional magic defense and some mp. They also take Ancient adena.. lots of ancient adena.
Enchanting skills is new to C4. You need an item called 'Secret Book of the Giants" and then take that to 'a certain NPC' to enchant your skills. I have not done this, so I don't know what happens next. The books sell for 4 million adena on my server, so I am not THAT curious.
You must unseal all your set items for the set bonus to apply. B-grade can be unsealed at any blacksmith (and resealed.) A-grade and S-grade can only be unsealed by the elusive Blacksmith of Mammon (A-grade can now be resealed.)
this brings me another question... a sealed item has some advantage that is lost unsealing it? i mean: you have to choose if using an unsealed one and having no set bonus but for ex more p.def, or unseal it and lose some p.def but have in excange the set bonus? or it's just you wanto to unseal it asap? :P
this brings me another question... a sealed item has some advantega that is lost unsealing it? i mean: you have to choose if using an unsealed one and having no set bonus but for ex more p.def, or unseal it and lose some p.def but have ini excange set bonus? or it's just you wanto to unseal it asap? :P
Nothing is lost in unsealing B-grade or A-grade. No stats are lost in unsealing S-grade, but you lose the ability to tailor it to your armor. If you unseal S-grade as a robe item, and then wish you'd made it a light-armor item, you can't switch back. B- and A-grade can now be resealed to switch them if you wish to.
Sealed item got an adventage to be unsealed into any type (robe, light, heavy). As of C4 it seems that this only matters for S grade since A grade can be resealed.